Field of the Invention
The present invention relates to an adaptive optical apparatus, an imaging apparatus, and a control method and program for the adaptive optical apparatus.
Description of the Related Art
Recently, an imaging apparatus (SLO: Scanning Laser Ophthalmoscope, to be also referred to as an SLO apparatus hereinafter) that two-dimensionally irradiates a fundus with a laser beam and receives the reflected light has been developed as an ophthalmic imaging apparatus. Also, an imaging apparatus has been developed (to be also referred to as an OCT apparatus hereinafter) using optical coherence tomography (OCT) that involves the interference of low-coherence light. In particular, the OCT apparatus is used to acquire a tomographic image of an object to be examined (for example, the fundus or its vicinity of an eye to be examined), because the apparatus can acquire a tomographic image with a resolution equivalent to about the wavelength of light entering an object to be examined.
Various kinds of OCT apparatuses have been developed such as a TD-OCT apparatus (Time Domain OCT) and an SD-OCT apparatus (Spectral Domain OCT). Recently, the resolution of particularly an ophthalmic imaging apparatus like this has been increased by increasing the NA (numerical aperture) of an irradiation laser. When imaging an object to be examined (for example, a fundus), however, the object must be imaged through eye optical tissues such as the cornea and crystalline lens. As the resolution increases, the aberrations of the cornea and crystalline lens exert a large influence on the image quality of an acquired image.
Accordingly, an AO-SLO apparatus (adaptive optics scanning laser ophthalmoscope) and AO-OCT apparatus have been studied that incorporate AO (Adaptive Optics) as an adaptive optical apparatus that measures the aberration of an object to be examined and corrects the aberration. The AO-SLO apparatus or AO-OCT apparatus generally measures the wavefront of an eye by using a wavefront sensor using the Shack-Hartmann wavefront sensor system. In the Shack-Hartmann wavefront sensor system, the wavefront aberration of an object to be examined is measured by irradiating the object with measurement light, and receiving the reflected light by a CCD (charge-coupled device) camera through a microlens array. An aberration correction device (a variable shape mirror or spatial phase modulator) is driven to correct the measured wavefront aberration, and the object to be examined is imaged through the device. Consequently, the AO-SLO apparatus and AO-OCT apparatus can perform high-resolution imaging.
An image acquisition apparatus including a general adaptive optical system performs feedback control that repeats a process of measuring the aberration of an eye and correcting the aberration by using the measurement result. Such a feedback process is beneficial because an error can occur between an instruction value for an aberration correction device and an actual correction amount, and the aberration can fluctuate due to a tear (i.e., water) in an eye or a change in the state of refraction. Aberration correction control is the same as general feedback control in that a predetermined time is necessary before an appropriate aberration correction state is reached after the start of processing. It takes a few seconds to a few tens of seconds before an appropriate correction state is obtained because the response speed of particularly a wavefront sensor or wavefront correction device used for aberration correction is low.
The position of an eye sometimes temporarily changes. In this state, the aberration measurement position in the eye is also changed, so the aberration measurement result is temporarily largely changed. As described above, the aberration is normally kept corrected by feedback control, but the eye's position often immediately returns to the original position. In this case, the aberration measurement result is largely changed again. This further prolongs the time required to reach an appropriate correction state.
Japanese Patent Laid-Open No. 2011-104125 has disclosed an ophthalmic apparatus that interrupts the control of an aberration correction device when it is detected that the eye's position has changed, and resumes the control of the aberration correction device from the interrupted state when the eye's position has returned to the original position.
The aberration measurement result is temporarily largely changed not only because the eye's position is changed, but also because an object that obstructs the measurement of the eye's aberration has entered between the pupil of the eye and the apparatus, for example, a blink of the eye has occurred.
More specifically, when the eyelid is closed by a blink of the eye, the measurement light cannot pass through the eyelid, so the aberration measurement result is temporarily changed to a large extent. As described previously, the aberration is normally kept corrected by feedback control. When an eye blink occurs, however, the eyelid immediately opens, so the aberration measurement result is changed by a large amount again. This further prolongs the time required to reach an appropriate correction state.
This present invention can shorten the time required to reach an appropriate correction state.